ci: Use half as many parallel softpipe / virgl test jobs

We're now using at least twice as many CPU cores per job (on shared
runners), so they only take about half as long, and should still be
under 10 minutes.

Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6011>

.gitlab-ci.yml

@@ -919,13 +919,12 @@ softpipe-gles2:
     DEQP_EXPECTED_RENDERER: softpipe
 
 softpipe-gles3:
-  parallel: 2
   variables:
     DEQP_VER: gles3
   extends: softpipe-gles2
 
 softpipe-gles31:
-  parallel: 4
+  parallel: 2
   variables:
     DEQP_VER: gles31
   extends: softpipe-gles2
@@ -948,14 +947,13 @@ virgl-gles2-on-gl:
     - .virgl-rules
 
 virgl-gles3-on-gl:
-  parallel: 2
   variables:
     DEQP_VER: gles3
     DEQP_RUNNER_OPTIONS: "--timeout 180"
   extends: virgl-gles2-on-gl
 
 virgl-gles31-on-gl:
-  parallel: 4
+  parallel: 2
   variables:
     DEQP_VER: gles31
     MESA_GLES_VERSION_OVERRIDE: "3.1"